This invention relates to a load plus pump control and more specifically to means for externally adjusting the minimum and maximum pump discharge pressures.
Some pump controls have the so-called load plus control function in which the pump discharge pressure is maintained at a higher level than the load pressure. Such controls commonly have a spring for exerting a biasing force on a valve and a load piston to increase the load on the spring in response to an increase in the load pressure. The preload on the spring is fixed at a preselected force for establishing the minimum pump discharge pressure while a fixed stop is provided to limit the maximum load on the spring to establish the maximum pump discharge pressure.
One problem encountered with such controls is that of setting the preload on the spring during assembly. Due to normal manufacturing tolerances, the preload on the spring in the assembled pump control may vary from one pump control to another. The normal manufacturing practice is to assemble the controls with several shims beneath the spring, operate the pump and measure the minimum and maximum pump discharge pressures. If either the minimum or maximum pump discharge pressure is not within the acceptable range, the pump controls must be disassembled and shims added or removed accordingly. The pump controls are commonly disassembled at least once and frequently several times before the preload on the spring is within acceptable limits. Such disassembling and reassembling of the pump control to adjust the preload on the spring is both time consuming and adds to the overall cost of manufacturing the pump control assembly.